1. Field of the Invention
The present invention relates to a process for the further processing of a residue remaining after vacuum distillation in a crude oil refinery and an apparatus therefor.
2. Description of the Background
Crude oil is conventionally processed in a refinery in a plurality of distillation stages. The first distillation stage proceeds at atmospheric pressure, and is followed by vacuum distillation at a pressure of about 10 to 30 mbar, which affords distillates having an atmospheric boiling point of up to about 570.degree. C. The low-value residue remaining after the vacuum distillation has a boiling point in excess of 570.degree. C. and contains, depending on the quality of the crude oil to be processed, a considerable proportion of the original crude oil feed. In recent years, an increase has been observed in the number of crude oils which yield an appreciable amount of vacuum residue. Therefore, further processing of this residue has become increasingly important.
The further processing of the vacuum residue is, at present, carried out either by solvent extraction or by cracking. Both processes are complex, however, and produce, in addition to the desired products, an economically worthless fraction of tar and coke. Both tar and coke are very inexpensive materials, and the amount thereof produced should be maintained as low as possible.
Swiss Patent 666 901 discloses a process in which the vacuum residue is further processed by being subjected to thin-layer short-path distillation. This process affords a comparatively large yield of valuable products, but is technically complex and costly. In addition, the use of complex additional equipment is required. Since the residue to be further processed has a very high temperature after vacuum distillation, it must be cooled prior to thin-film short-path distillation; i.e., its heat content cannot be usefully utilized in full.
Thus, a need exists for a process which is less complex in terms of equipment required, and which, at the same time, offers an increased yield of heavy vacuum gas oil and a reduced amount of tar-like residue remaining.